Acoustical gypsum board for ceiling panel

ABSTRACT

Low density acoustical gypsum boards having a perforated cover sheet that have good sound absorption properties and are generally clear of falling gypsum dust. The invention optionally provides a cover sheet having a pattern producing a textured visual effect particularly when viewed from a distance. The acoustical gypsum boards can be produced on modified existing gypsum board lines.

FIELD OF THE INVENTION

The present invention relates to a lightweight gypsum board suitable foruse as a soundproofing or acoustical panel. The invention provideseconomical and convenient-to-use low density acoustical gypsum boardshaving sound absorbing characteristics on a par with conventionalacoustic panels and a method for their preparation.

BACKGROUND OF THE INVENTION

Acoustical panels are used to form soundproofing interior surfaces. Theytypically come in the form of ceiling panels, wall panels, andpartitions (e.g., partitions between office cubicles), and are used incommercial buildings, residential buildings, public buildings,auditoriums, etc. The panels are generally planar and include acousticalcharacteristics derived from the materials selected for theirmanufacture and from their ability to accept sound absorbing perforationwithout adversely affecting their durability.

Most common acoustical panels are mineral wool-based, and may alsoinclude fiberglass, expanded perlite, paper fiber, and binders such asstarch. Mineral wool is the most prevalent and important ingredient insuch prior acoustical panels. Mineral wool-based acoustical panels arevery porous which accounts for their good sound absorption. Fillers,such as expanded perlite, may be incorporated into mineral wool-basedacoustic panels to reduce the weight of the final product. In addition,mineral wool-based acoustical panels are commonly perforated in order tofurther increase their sound absorption.

Currently, acoustical panels are prepared in a manner similar to thoseused in conventional papermaking processes by water-felting diluteaqueous dispersions of mineral wool, perlite, binder, and otheringredients as desired. In such processes, the dispersions flow onto amoving foraminous support wire, such as that of a Fourdrinier or Olivermat-forming machine for dewatering, as will be appreciated by one ofordinary skill in the art. The dispersions are dewatered first bygravity drainage and then by vacuum suction. The resulting dewatered butyet wet mat is dried in a convection oven, the dried material is cut todesired dimensions, and multiple coatings are applied to obtain thefinished panel.

Acoustical panels also can be made by a wet pulp molding or cast processsuch as described in U.S. Pat. No. 1,769,519. In accordance with thisprocess, a molding composition comprising granulated mineral woolfibers, fillers, colorants, a binder such as cooked starch, and water,is prepared for molding or casting the panel. The composition is placedupon suitable trays that have been covered with paper or a paper-backedmetallic foil and then the composition is screeded to a desiredthickness with a forming plate. A decorative surface, such as a surfacewith random elongated fissures, also may be provided by a screed bar orpatterned roll. The trays filled with the mineral wool composition arethen placed in an oven to dry.

Both water felting and tray casting techniques for preparing acousticalpanels are not entirely satisfactory because of their complexity andexpense. In addition to raw material costs, these processes requirelarge amounts of water and energy. Furthermore, panels preparedaccording to these methods may be subject to sagging, especially if thepanels are stored under conditions of high humidity or when the panelsare installed horizontally on widely spaced supporting members. Thetendency to sag is aggravated by the presence of hygroscopic binderssuch as recycled paper fiber or starch. In addition, several surfacecoatings are generally required in order to achieve a proper appearancein the final acoustical panel, due to the absorbency of the materialsused. Furthermore, where the panels are perforated care must be takennot to cover or clog the perforated holes with the final coatings. Forexample, after perforation, coatings must be applied by spraying ratherthan simpler, less expensive roller-applied coating processes to avoidclogging of the perforated holes.

Conventional gypsum wallboard, which comprises set gypsum (calciumsulfate dihydrate), sandwiched between paper cover sheets, is commonlyused in construction applications because of its durability, fireresistant characteristics and economy. However, such paper coveredgypsum wallboard has not in the past been considered for use inacoustical ceiling panels for a number of reasons. First, such gypsumwallboard does not inherently have good sound absorption properties.Even if it is punched or perforated in the same manner as conventionalmineral wool-based acoustical panel, little or no significant soundabsorption improvement is achieved. Furthermore, punching conventionalpaper covered gypsum wallboard causes substantial amounts of gypsum dustto loosen and fall from the perforated holes. (Conventional acousticalpanels also can exhibit some dust (powder) loss.) Also, conventionalgypsum wallboard may be heavy, ca. 40 lbs/ft³ (“pcf”), and this weightmakes conventional wallboard unsuitable in most acoustical applications.Even the recently developed lightweight gypsum board described in U.S.Pat. No. 5,922,447 to the present inventor, Mirza A. Baig, typically hasa density greater than or equal to about 21 pcf, which exceeds thetypical densities of conventional mineral wool based acoustical panelsof about 12-20 pcf. Therefore, the problems of lack of sound absorption,high density, and gypsum dust loss have discouraged the use of eitherconventional or lightweight face-sheeted gypsum board in acoustic tileapplications.

One type of tray cast gypsum-based acoustical panel is discussed in U.S.patent application Publication 2004/0231916A1 to Englert et al. Thisapplication is primarily directed to panels that, unlike conventionalwallboard preferably have no top face paper layer. In a less preferredembodiment of Englert et al. a top face paper is used but there is nosuggestion to perforate after drying, which is not surprising becauseperforating this dried board would be expected to produce substantialdust loss.

The prior art conventional gypsum wallboard is flat and smooth, havingno significant visual surface texture. Known acoustical panels, on theother hand, typically have a substantial three-dimensional texture. If away could be found to produce acoustical gypsum boards that achieve thesame visual effect (and sound absorption properties) as are found inconventional mineral-wool based acoustical panels without actuallyadding texture and thereby damaging the outer surface of the face paperof the boards, this would be yet another useful contribution to the art.

Therefore, it would be advantageous if a way could be found to makeconventionally produced gypsum wallboard type products of sufficientlylow density and sufficiently good sound absorbing properties to beuseful in acoustical applications. It would be particularly advantageousif a way could be found to make such gypsum wallboard type productshaving acceptable sound absorption properties that are not subject tothe problem of falling gypsum dust, that achieve the same visual effectas known textured acoustical panels, and that also have resistance tosag equal to or better than conventional mineral wool-based ceilingpanels.

BRIEF SUMMARY OF THE INVENTION

The present invention comprises low density acoustical gypsum boards,having top and bottom cover sheets, that are relatively inexpensive tomanufacture, and that can be produced efficiently in large quantities onan existing gypsum board line. These low density acoustical gypsumboards resist permanent deformation, such as sag, and have soundabsorption properties on a par with conventional acoustical panels. Thelow density acoustical gypsum boards are perforated and are not subjectto the problem of falling gypsum dust. Furthermore, the inventionoptionally provides a top cover sheet to which a visual pattern has beenapplied in order to make the surface appear to be textured, particularlywhen viewed from a distance (i.e. when viewed by a person standing onthe floor of a room looking up at the ceiling). These and otheradvantages of the present invention, as well as additional inventivefeatures, will be apparent from the description of the inventionprovided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a cut-away end view of a lowdensity acoustical gypsum board in accordance with the inventionincluding top and bottom cover sheets, a set gypsum core, andperforations extending across the top cover sheet and into the setgypsum core;

FIG. 2 is a plan view of a top cover sheet (face paper) having a patternas printed on the face paper cover sheet used in one embodiment of thepresent invention; and

FIG. 3 is a plan view of the top cover sheet of the low densityacoustical gypsum board of FIG. 1 showing the printed pattern of FIG. 2and including small circular puncture holes extending through the facepaper and into the set gypsum core.

DETAILED DESCRIPTION OF THE INVENTION

In one embodiment of the invention, low density acoustical gypsum boardsof this invention include a set gypsum core structure made using a coreformulation including calcium sulfate hemihydrate (“stucco”), perlite,paper fiber, and starch. The set gypsum core of the low densityacoustical gypsum boards is sandwiched between two substantiallyparallel top and bottom cover sheets, such as paper cover sheets, toprovide substantially flat, planar, top and bottom surfaces. Inaddition, the low density acoustical gypsum boards include perforationsformed through the top (outer) surface of the board that extend throughthe cover sheet and into the set gypsum core. In a preferred embodiment,the perforations are generally well-formed small circular holes thatextend generally perpendicularly to the top outer surface of the boardthrough the top cover sheet and into the set gypsum core. In anotherpreferred embodiment, the exposed surface of the perforated top coversheet is printed with a pattern. The low density acoustical gypsumboards are manufactured generally in the same fashion as conventionalwallboard, modified as discussed below.

Preferably, the low density acoustical gypsum board of the presentinvention exhibits a Noise Reduction Coefficient (NRC) of at least about0.5, according to ASTM C 423-02, and more preferably, a Noise ReductionCoefficient at or near 1.0. In some embodiments, the low densityacoustical gypsum board demonstrates a Noise Reduction Coefficientaccording to ASTM C 423-02 of at least about 0.55 up to a yet morepreferable NRC of at least about 0.7.

Now turning to FIG. 1, there is provided a low density acoustical gypsumboard 10 according to one embodiment of the present invention. Theacoustical gypsum board 10 includes a set gypsum core 12 having a topsurface 14 and a bottom surface 16. The set gypsum core 12 is formedbetween a face cover sheet 20 and a back cover sheet 30 with the coversheets (20, 30) bonded to the core. A multiplicity of perforations 40extend through the face cover sheet 20 and the top surface 14 into theset gypsum core 12.

FIG. 2 illustrates an exemplary pattern 50 according to one embodimentof the present invention that is applied to the outer surface of a facecover sheet 20 a. In this example, the pattern creates a visualappearance of texture to the human eye when viewed from a sufficientdistance or perspective, for example by a person standing on the floorof a room looking up at the ceiling.

FIG. 3 is a plan view of the low density acoustical gypsum board 10 ofFIG. 1 covered on its top surface by the pattern-bearing face coversheet 20 a of FIG. 2 and including a multiplicity of perforations 40formed through face cover sheet 20 a and into set gypsum core 12.

Set gypsum core 12 is made from an aqueous slurry of the key corecomponents listed below in Table 1. Other conventional ingredients thatmay be added to the slurry, such as dispersants, strength additives(e.g. metaphosphates), and accelerators, are described generally below.TABLE 1 CORE FORMULATION RANGES Amount in weight % Preferred amount inComponent (wt % solids)¹ weight %¹ Stucco 75-90 80-85 Perlite  0-15 5-8Paper (cellulose fiber) 2.0-12   6-10 Starch 0.5-5.0 0.5-2  Water/solids ratio 2.0-3.5 2.3-2.5¹This embodiment of the core formulation is based on 100% solids ofthese four key ingredients.

The acoustical gypsum board of the present invention has a board densityof not more than about 20 pcf. In a preferred embodiment, the acousticalgypsum board of the present invention has a board density of about 17 toabout 19 pcf, and most preferably the acoustical gypsum board of thepresent invention will have a board density of not more than about 16pcf.

It is preferred that perlite be used in the core formulations (to helplower board density), although in a less preferred embodiment, the coreformulation can be free of perlite. The presence of perlite in the coreformulation, however, reduces estimated Noise Reduction Coefficient(NRC) values of the final acoustical gypsum boards. Paper fiber, on theother hand, can also be used in core formulations to achieve yet lowerboard density while at the same time providing increased NRC values,offsetting the detrimental loss of noise reduction caused by theperlite. Therefore, in preferred embodiments, as discussed below, risingperlite levels are balanced with increased levels of paper fiber.

In a preferred embodiment, perlite will be used in an amount of at leastabout 5% by weight of the core formulation. Additionally in thispreferred embodiment, both perlite and paper fiber must be present inthe core formulation, and the weight ratio of perlite to paper fiberwill range from about 1:1.1 to about 1:2. In a yet more preferredembodiment, the weight ratio of perlite to paper fiber will range fromabout 1:1.4 to about 1:1.6.

For example, in one embodiment, the core formulation comprises, based onthe total weight of the core formulation: stucco 85% by weight; perlite5% by weight; paper fiber 8% by weight; and starch 2% by weight.The weight ratio of perlite to paper fiber is 1:1.6. By incorporating asoap foam (discussed below) having a foam density of 10 pcf (over andabove the 100% solids weight % total of the core formulation itself),this core formulation can be used to make an acoustical gypsum boardhaving a density as low as about 17.0 pcf. Other additives can beincluded over and above the 100% solids weight % total of the coreformulation itself (i.e. accelerators, dispersants, and strengthadditives as discussed below).

The low density acoustical gypsum boards of the present invention mustbe perforated to produce a multiplicity of perforations that aresubstantially clear of gypsum dust or powder. That such clearperforations can be achieved is quite unexpected given that whenconventional gypsum boards are perforated in the same manner, asubstantial amount of gypsum dust is released. The perforations inboards of the present invention are illustrated, for example, in FIGS. 1and 3. As shown there, the acoustical gypsum board is perforated throughthe face paper to produce holes extending into the set gypsum core, butnot passing through the back paper. The orientation of the holes is, asshown, preferably generally perpendicular to the planar surface of thefirst cover sheet, or face paper. Thus, in a key aspect, the overall setgypsum core provides sound absorption properties in the low densityacoustical gypsum boards when combined with perforations substantiallyclear of gypsum dust.

The low density acoustical gypsum boards may be punched using aperforation pin count (100% sharp pins) of about 1800 pins per squarefoot, pin diameter 0.062 in. Other pin counts and pin diameters can beused, as will be recognized by those skilled in the art. For example, apin count of about 1850 per square foot, of about 1750 per square foot,or of about 1566 per square foot could be used, and pin diameters ofabout 0.050 in. and about 0.045 in. could be used. Also, any type of pinmay be used, including sharp, blunt, or combinations thereof. It will beappreciated by one skilled in the art that pin count can be varied, andpin type, style, and diameter can be varied, or used in variouscombinations, in order to achieve the desired sound reductionproperties. The depth of the perforated holes can range from about ¼inch to about ½ inch.

The boards can be made, and punched, according to a batch process or ina continuous process. The punching, or perforation step, can be appliedas part of a standard commercial wallboard production line, followingthe drying of the paper-covered board product.

Cover sheets 20 and 30 may be made of paper as in conventional gypsumwallboard, although other useful cover sheet materials known in the artmay be used. Paper cover sheets provide strength characteristics in theacoustical gypsum board. Useful cover sheet paper includes Manila 7-plyand News-Line 7-ply, available from United States Gypsum Corporation,Chicago, Ill.; and Grey-Back 3-ply and Manila Ivory 3-ply, availablefrom Caraustar, Newport, Ind. The paper cover sheets comprise top coversheets, or face paper, and bottom cover sheets, or back paper. Apreferred back cover sheet paper is News-Line. A preferred face coversheet paper is Manila 7-ply.

Gypsum-based products have the tendency to sag under conditions of highhumidity. The proper choice of back paper helps reduce sag in thefinished acoustical gypsum board. A preferred back paper for thispurpose in the low density acoustical gypsum boards of the presentinvention is News-Line 7-ply. In addition, strength additives such assodium trimetaphosphate, may be added to the core formulations tofurther reduce sag. Also, a formaldehyde-based coating can be applied tothe back paper of the acoustical gypsum boards to further reduce sag.

The face paper can be used plain, or with a pattern applied to it, asdiscussed above and shown in FIG. 2. Many variations of pattern andpattern color may be used on the face paper. Tinted papers can also beused as appropriate, and color printing or inks can be employed to applythe pattern. The pattern as shown in FIG. 2, as well as other patterns,can be made by taking a photo of a given design and printing the designon the face paper. Also, printing of the face paper can be done on-lineduring the production process, preferably after the face paper is dried.In addition, after printing the pattern, a protective coating can beapplied on the outer surface of the face paper to protect the printedpattern from abrasion and environmental conditions.

A soap foam is required in making the low density acoustical gypsumboards of the present invention, in order to reduce the density of thefinal board. The soap foam density can range from about 5.0 pcf to about12.0 pcf, a preferred soap foam density is about 10 pcf, to achieve afinal board density of not more than about 20 pcf. The soap foam is usedin an amount over and above the 100% solids weight % total of the coreformulation itself. For example, a soap can be used in an amount ofabout 2 g to about 3 g per about 1000 g total solids (or about 0.2% toabout 0.3% by weight based on total solids) when used to make the soapfoam and added to the core formulation as in Table 1 over and above the100% solids weight % total of the core formulation itself. Useful soapsfor making the soap foam include FA 403-Agent X-2332 available fromStepan Chemical Company, Northfield, Ill.

The bond between a set gypsum core and the paper cover sheets may beadversely affected by the presence of foam in the core formulation.Since approximately ⅓ of the gypsum boards by volume may consist offoam, the foam can interfere with the bond between the set gypsum coreand the paper cover sheets. Thus, a non-foamed bonding layer may beprovided on the set gypsum core-contacting surfaces of both the facepaper and the back paper prior to forming the gypsum boards. This layerformulation is commonly the same as the core formulation, except thatthe foam is omitted. In order to form this layer, foam can bemechanically removed from the core formulation, or a different foam-freeformulation can be applied at the set gypsum/face paper interface.

The primary component of the core formulation is calcium sulfatehemihydrate or calcined gypsum, also referred to as stucco. The calcinedgypsum can be in the form of alpha calcium sulfate hemihydrate, betacalcium sulfate hemihydrate, water-soluble calcium sulfate anhydrite, ormixtures thereof. In preferred embodiments, the calcined gypsum is inthe form of beta calcium sulfate hemihydrate. A useful calcined gypsumis CKS dry stucco, available from United States Gypsum Corp., Chicago,Ill. The calcined gypsum is present in an aqueous slurry of the coreformulation in an amount sufficient to allow for the formation of aninterlocking matrix of set gypsum in the final paper-covered board. Inthe core formulation used to make the set gypsum core, stucco is presentin an amount ranging from about 75% to about 90% by weight based on thetotal (solids) weight of the core formulation; preferably, the stucco ispresent in an amount ranging from about 80% to about 85% by weight basedon the total weight of the core formulation.

As noted earlier, it is preferred that perlite is used in the coreformulation. In the core formulation used to make the set gypsum core,perlite can be present in an amount up to about 15% by weight based onthe total (solids) weight of the core formulation; preferably, perliteis present in an amount ranging from about 5% to about 8% by weightbased on the total weight of the core formulation.

In the practice of the invention, the perlite density must be in therange of about 3 to about 8.5 pcf. The perlite can be obtained from anumber of commercial sources. In the examples described below, Type 3-Sbrand perlite available from Silbrico located in Hodgkins, Ill., wasused. This perlite typically has a density of about 3 to about 5.0 pcf.

Perlite is a form of glassy rock similar to obsidian. It generallycontains 65-75% SiO₂, 10-20% Al₂O₃, 2-5% H₂O, and smaller amounts ofsoda, potash, and lime. When perlite is heated to its softening point,it expands to form a light fluffy material similar to pumice. Inpreparing the perlite for use in the present invention it is firstground to a size finer than minus 200 mesh. The ground perlite is thenheated to a temperature of about 1500°-1800° F., and preferably about1750° F. This process is carried out in a perlite expander by firstheating the air and then introducing the finely ground perlite into theheated air. As it is carried by the air, it is heated and pops likepopcorn to form expanded perlite. Expanded perlite contains many finecracks and fissures, and, when placed in contact with water, the waterpenetrates the cracks and fissures and enters into the air filledcavities of the perlite, thereby greatly increasing the weight of theparticles.

For the purposes of the present low density acoustical panel, it isimportant that the perlite not be coated or treated in any way whichwill make the individual perlite particles watertight or even waterresistant. If so, the water resistant coating or treatment will resultin non-uniform distribution of the perlite in the aqueous slurry of thecore formulation, and it will also be more difficult, if not impossible,for the gypsum crystals to penetrate and interlock with the perliteparticles.

Paper fiber must be used in the core formulation. A useful form of paperfiber is hydropulp newsprint or hydropulped waste paper. Othercellulosic fibrous materials can be used, alone or in combination withhydropulped paper fiber, such as wood fiber or dry fiberized gypsumwallboard paper or Kraft paper. In the core formulation used to make theset gypsum core, paper fiber is present in an amount ranging from about2% to about 12% by weight based on the total (solids) weight of the coreformulation; preferably, paper fiber is present in an amount rangingfrom about 6% to about 10% by weight based on the total weight of thecore formulation.

Starch must be used in the core formulation. For example, wheat starchcan be used. In another embodiment, pearl starch can be used, which is aknown combination of starch made from corn, potato, and/or wheat stock.The starch may be provided in raw form or partially or fully cookedseparately prior to mixing with the core formulation. Partial cooking inthe present process is considered to occur once the starch and waterslurry temperature reaches 150° F. The starch is considered to be fullycooked once the starch slurry reaches a temperature of at least 185° F.Through partial or full cooking, pearl starch is converted from beingmigrating in nature to being non-migrating in nature. Whennon-migrating, the starch is retained in the core portion of the boardprior to setting. The presence of the starch in the core also aids inthe binding of the face paper to the core. Alternate sources of starchwhich are also contemplated are acid-modified starches including Gypsetmade by Ogilive, located in Montreal, Canada, and LC-211, a commonstarch made from flour, supplied by Archer Daniels Midland of DodgeCity, Kans. In the latter two cases, the starches are of the migratingtype. Another useful starch is acid-modified corn flour, available asHI-BOND from Bunge, St. Louis, Mo. This starch has the following typicalanalysis: moisture 10.0%, oil 1.4%, solubles 17.0%, alkaline fluidity98.0%, loose bulk density 30 lb/ft³, and a 20% slurry producing a pH of4.3.

Pregelatinized starch in particular, can be used in slurries prepared inaccordance with the core formulations as in Table 1. A preferredpregelatinized starch is pregelatinized corn starch, for examplepregelatinized corn flour available from Bunge, St. Louis, Mo., havingthe following typical analysis: moisture 7.5%, protein 8.0%, oil 0.5%,crude fiber 0.5%, ash 0.3%; having a green strength of 0.48 psi; andhaving a loose bulk density of 35.0 lb/ft³. In the core formulation usedto make the set gypsum core, starch is present in an amount ranging fromabout 0.5% to about 5% by weight based on the total (solids) weight ofthe core formulation; preferably, starch is present in an amount rangingfrom about 0.5% to about 2% by weight based on the total weight of thecore formulation.

Accelerators can be added to the core formulations of the presentinvention, for example, wet gypsum accelerator (WGA), as described inU.S. Pat. No. 6,409,825 to Yu et al., herein incorporated by reference.One desirable heat resistant accelerator (HRA) can be made from the drygrinding of landplaster (calcium sulfate dihydrate). Small amounts ofadditives (normally about 5% by weight) such as sugar, dextrose, boricacid, and starch can be used to make this HRA. Sugar or dextrose arecurrently preferred. Another useful accelerator is “climate stabilizedaccelerator” or “climate stable accelerator,” (CSA) as described in U.S.Pat. No. 3,573,947, herein incorporated by reference. For example, anaccelerator (HRA or CSA) can be used in an amount of about 5 g/1000 gtotal solids (or about 0.5% by weight based on total solids) when addedto the core formulation as in Table 1 over and above the 100% solidsweight % total of the core formulation itself.

Dispersants can be added to the core formulations of the presentinvention. Useful dispersants include polynaphthalenesulfonates andBOREM, available from Boremco Laboratories, River Falls, Mass. Forexample, a dispersant can be used in an amount of about 0.9 g/1000 gtotal solids (or about 0.1% by weight based on total solids) when addedto the core formulation as in Table 1 over and above the 100% solidsweight % total of the core formulation itself.

The naphthalenesulfonate dispersants that may be used in the presentinvention include polynaphthalenesulfonic acid and its salts(polynaphthalenesulfonates) and derivatives, which are condensationproducts of naphthalenesulfonic acids and formaldehyde. Particularlydesirable polynaphthalenesulfonates include sodium and calciumnaphthalenesulfonate. The average molecular weight of thenaphthalenesulfonates can range from about 3,000 to 20,000, although itis preferred that the molecular weight be about 8,000 to 10,000. Ahigher molecular weight dispersant has higher viscosity, and generates ahigher water demand in the formulation. Useful naphthalenesulfonatesinclude LOMAR D, available from Henkel Corporation, DILOFLO, availablefrom GEO Specialty Chemicals, Cleveland, Ohio, and DAXAD, available fromHampshire Chemical Corp., Lexington, Mass. It is preferred that thenaphthalenesulfonates be used in the form of an aqueous solution, forexample, in the range of about 40-45% by weight solids content.

Useful polynaphthalenesulfonates have the general structure (I):

wherein n is >2, and wherein M is sodium, potassium, calcium, and thelike.

For example, a polynaphthalenesulfoante dispersant can be used in anamount of about 0.9 g/1000 g total solids (or about 0.1% by weight basedon total solids) when added to the core formulation as in Table 1 overand above the 100% solids weight % total of the core formulation itself.

Strength additives can be added to the core formulations of the presentinvention, for example, metaphosphates such as sodium trimetaphosphate.Any suitable water-soluble metaphosphate or polyphosphate can be used inaccordance with the present invention. It is preferred that atrimetaphosphate salt be used, including double salts, that istrimetaphosphate salts having two cations. Particularly usefultrimetaphosphate salts include sodium trimetaphosphate, potassiumtrimetaphosphate, calcium trimetaphosphate, sodium calciumtrimetaphosphate, lithium trimetaphosphate, ammonium trimetaphosphate,and the like, or combinations thereof. A preferred trimetaphosphate saltis sodium trimetaphosphate. It is preferred to use the trimetaphosphatesalt as an aqueous solution, for example, in the range of about 10-15%by weight solids content. Other cyclic or acyclic polyphosphates canalso be used, as described in U.S. Pat. No. 6,409,825 to Yu et al.,herein incorporated by reference. For example, sodium trimetaphosphatecan be used in an amount of about 0.9 g/1000 g total solids (or about0.1% by weight based on total solids) when added to the core formulationas in Table 1 over and above the 100% solids weight % total of the coreformulation itself.

As shown in the following examples, low density acoustical gypsum panelswere prepared using the core formulations of Table 1. Except whereindicated, Manila 7-ply paper, either plain or with an applied pattern,was used as the top cover sheet or face sheet. A non-foamed bondinglayer (as described above) was applied to the set gypsum core-contactingsurfaces of both the back paper and the face paper. The averagethickness of the panels was 0.54 inch. In addition, each acousticalgypsum board was perforated through the face sheet. The perforationdepth was ½ inch (except as indicated), and the perforation pin count(100% sharp pins) was 1800 pins per square foot, pin diameter 0.062 in.

In the following examples, certain additives were included in the coreformulation as in Table 1 over and above the 100% solids weight % totalof the core formulation itself. The following additive levels wereincluded in all of the examples: accelerator (HRA or CSA) at 0.5% byweight based on total solids; dispersant at 0.1% by weight based ontotal solids; and sodium trimetaphosphate at 0.1% by weight based ontotal solids. Additionally, in each example below (except as indicated),soap foam at a density of 10 pcf was incorporated into the coreformulations.

EXAMPLE 1A

Preparation of Low density acoustical gypsum board

Sample low density acoustical gypsum boards were prepared by a castingprocess in accordance with U.S. Pat. No. 5,922,447 using the coreformulations of Table 1 with a high density soap foam (e.g. 10 pcf)incorporated into slurry of the core formulation.

EXAMPLE 1B

Preparation of Low density acoustical gypsum board by a continuousprocess

Sample low density acoustical gypsum boards were prepared by acontinuous process in accordance with U.S. Pat. No. 6,342,284 to Yu etal. and U.S. Pat. No. 6,632,550 to Yu et al., herein incorporated byreference. This includes the separate generation of a high density foam(e.g. 10 pcf) and introduction of the foam into the slurry of the otheringredients as described in Example 5 of these patents.

EXAMPLE 2

Low density acoustical gypsum board—assessment of paper fibers and highdensity foam

Step 1. The following core formulations were prepared as an aqueousslurry as shown in Table 2. TABLE 2 Slurry formula: Board Board BoardBoard Formula 1 Formula 2 Formula 3 Formula 4 (weight % (weight %(weight % (weight % Component solids) solids) solids) solids) Stucco85.6 85.6 85.6 85.6 Perlite 5.0 5.0 5.0 5.0 Dry paper fiber 7.4 3.7 1.90 Wet paper fiber 0 3.7 5.6 7.4 Total paper fiber 7.4 7.4 7.4 7.4 Starch2.0 2.0 2.0 2.0 Water/solids ratio 2.5 2.7 2.4 2.7Dry paper fiber: fiberized gypsum wallboard paperWet paper fiber: hydropulped waste paperAdditives were included in addition to the above total solids:accelerator (HRA or CSA) at 0.5% by weight based on total solids;dispersant at 0.1% by weight based on total solids; and sodiumtrimetaphosphate at 0.1% by weight based on total solids.

Soap foam for each formulation sample was prepared as follows. Soap (2.0g), available as product FA 403-Agent X-2332 from Stepan ChemicalCompany, Northfield, Ill., was mixed with water (148 g) in a high shearHamilton Beach blender for 10 seconds. The resulting foam volume was 900ml; the foam density was 10 pounds per cubic foot. This soap foam wasincorporated into the core formulations of Table 2.

Step 2. Sample boards were prepared by casting as in Example 1A usingthe core formulations of Table 2, and perforated, as discussed above.The perforation depth was ½ inch, and the perforation pin count (100%sharp pins) was 1800 pins per square foot, pin diameter 0.062 in. TABLE3 Properties Board 1 Board 2 Board 3 Board 4 Thickness, inch 0.545 0.5450.545 0.545 Density, pcf 17.5 16.7 18.0 17.5 Weight, lb/MSF 795 758 818795 Water evaporation, 1519 1519 1475 1486 lb/MSF Estimated NRC 0.610.55 0.54 — Dust, g/MSF 768 182 192 240“MSF” is a standard abbreviation in the art for a thousand square feet.

As shown in Table 3, the sample boards have densities lower than 20 pcfand acceptable NRC values. Also, in Boards 2-4 dust was significantlyreduced.

EXAMPLE 3

Low density acoustical gypsum board—assessment of paper cover sheets,paper fibers and high density foam

The following core formulation was used to make the aqueous slurry(solids by weight %): stucco 86.5% perlite 5.0% paper fiber (hydropulp)6.5% pregelatinized com starch 2.0%.

As in Example 2, a soap foam having a foam density of 10 pcf was used.Additional additives were included in addition to the above totalsolids: CSA at 0.5% by weight based on total solids; Borem at 0.1% byweight based on total solids; and sodium trimetaphosphate at 0.1% byweight based on total solids. The sample boards were cast, andperforated, as in Step 2 of Example 2. The perforation depth was ½ inch,and the perforation pin count (100% sharp pins) was 1800 pins per squarefoot, pin diameter 0.062 in. TABLE 4 Components Board 5 Board 6 Board 7Board 8 Face paper 7-ply 7-ply 3-ply 3-ply Manila Manila Manila/IvoryManila/Ivory Back paper 7-ply 7-ply 7-ply 7-ply News-line News-lineNews-line News-line Water/solids ratio 2.3 2.4 2.3 2.4 PropertiesThickness, inch 0.555 0.555 0.555 0.555 Density, pcf 19.0 17.3 17.8 17.2Weight, lb/MSF 879 800 823 796 Water evaporation, 1596 1526 1543 1526lb/MSF Estimated NRC 0.45 0.55 0.44 0.46 Dust, g/MSF 173 134 160 200

As shown in Table 4, the sample boards have densities lower than 20 pcf,and no significant difference was observed in NRC values using 7-ply or3-ply sheets on the top surface of the board. However, reduction of thepaper fiber level reduced NRC values. Dust levels were acceptable incomparison to conventional acoustical panel (300 g/MSF), as discussedabove.

EXAMPLE 4

Low density acoustical gypsum board—assessment of printed paper coversheets and high density foam

Step 1. The following core formulations were prepared as an aqueousslurry as shown in Table 5. TABLE 5 Slurry formula: Board Formula 9Board Formula 10 Board Formula 11 Board Formula 12 Component (weight %solids) (weight % solids) (weight % solids) (weight % solids) Stucco85.0 84.2 85.0 84.0 Perlite 5.0 4.9 5.0 5.0 Paper fiber (hydropulp) 8.08.0 8.0 8.0 Starch 2.0 3.0 2.0 3.0 Foam¹ density, pcf 10.0 10.0 10.010.0 Water/solids ratio 2.4 2.4 2.4 2.4 Face paper Manila ManilaManila - printed Manila - printed w/ pattern of FIG. 2 w/ pattern ofFIG. 2Additives were included in addition to the above total solids:accelerator (HRA or CSA) at 0.5% by weight based on total solids;dispersant at 0.1% by weight based on total solids; and sodiumtrimetaphosphate at 0.1% by weight based on total solids.¹Soap foam prepared as in Ex. 2

Step 2. Sample boards were prepared by casting as in Step 2 of Example2, using the core formulations of Table 5, and perforated, as discussedabove. The perforation depth was ½ inch, and the perforation pin count(100% sharp pins) was 1800 pins per square foot, pin diameter 0.062 in.TABLE 6 Properties Board 9 Board 10 Board 11 Board 12 Set time, min.11.0 11.0 11.0 11.0 Thickness, inch 0.550 0.550 0.550 0.550 Density, pcf18.1 17.4 17.8 18.2 Weight, lb/MSF 830 798 816 834 Water evaporation,1570 1695 1496 1568 lb/MSF Estimated NRC 0.58 0.52 0.53 0.55

As shown in Table 6, the sample boards have densities lower than 20 pcfand acceptable NRC values. No negative impact was observed on NRC valuesusing either plain or printed face paper.

EXAMPLE 5

Low density acoustical gypsum board—assessment of 3-ply and 7-plyprinted paper cover sheets and high density foam

Step 1. The following core formulations were prepared as an aqueousslurry as shown in Table 7. TABLE 7 Slurry formula: Board Board BoardBoard Board Formula 13 Formula 14 Formula 15 Formula 16 Formula 17Component (wt % solids) (wt % solids) (wt % solids) (wt % solids) (wt %solids) Stucco 85.0 84.0 85.0 84.0 84.0 Perlite 5.0 5.0 5.0 5.0 5.0Paper fiber (hydropulp) 8.0 8.0 8.0 8.0 8.0 Starch 2.0 3.0 2.0 3.0 3.0Foam density, pcf 10.0¹ 10.0¹ 10.0¹ 10.0¹ 10.0² Water/solids ratio 2.42.4 2.4 2.4 2.4 Face paper Manila 3-ply - Manila 3-ply - Manila 7-ply -Manila 7-ply - Manila 7-ply printed printed printed printed w/ patternof w/ pattern of w/ pattern of w/ pattern of FIG. 2 and FIG. 2 andcoated coatedAdditives were included in addition to the above total solids:accelerator (HRA or CSA) at 0.5% by weight based on total solids;dispersant at 0.1% by weight based on total solids; and sodiumtrimetaphosphate at 0.1% by weight based on total solids.¹Soap foam prepared as in Ex. 2²Higher amount of soap foam - prepared as in Ex. 2 using 3.0 g soap and222 g water

Step 2. Sample boards were prepared by casting as in Step 2 of Example2, using the core formulations of Table 7, and perforated, as discussedabove. The perforation depth was ½ inch, and the perforation pin count(100% sharp pins) was 1800 pins per square foot, pin diameter 0.062 in.TABLE 8 Properties Board 13 Board 14 Board 15 Board 16 Board 17 Settime, 11.0 11.0 11.0 11.0 min. Thickness, 0.555 0.555 0.555 0.555 0.555inch Density, pcf 16.4 17.2 18.0 18.1 15.9 Weight, 759 796 833 837 735lb/MSF Water 1354 1467 1477 1496 1388 evaporation, lb/MSF Estimated 0.530.55 0.54 0.53 0.59 NRC

As shown in Table 8, the sample boards have densities lower than 20 pcfand acceptable NRC values. For boards 13-16, no negative impact wasobserved on NRC values using either 3-ply printed paper or 7-ply printedand coated paper. For board 17, an increased amount of high density soapfoam produced lower board density and increased the NRC value.

EXAMPLE 6

Low density acoustical gypsum board—assessment of printed paper coversheets, paper fibers, perlite, and high density foam

Step 1. The following core formulations were prepared as an aqueousslurry as shown in Table 9. TABLE 9 Slurry formula: Board Formula 17Board Formula 18 Component (weight % solids) (weight % solids) Stucco81.9 80.0 Perlite 7.0 7.0 Paper fiber (hydropulp) 8.1 10.0 Starch 3.03.0 Foam¹ density, pcf 10.0 10.0 Water/solids ratio 2.5 2.5 Face paperManila - printed Manila - printed w/pattern of FIG. 2 w/ pattern of FIG.2Additives were included in addition to the above total solids:accelerator (HRA or CSA) at 0.5% by weight based on total solids;dispersant at 0.1% by weight based on total solids; and sodiumtrimetaphosphate at 0.1% by weight based on total solids.¹Soap foam prepared as in Ex. 2

Step 2. Sample boards were prepared by casting as in Step 2 of Example2, using the core formulations of Table 9, and perforated, as discussedabove. The perforation depth was ½ inch, and the perforation pin count(100% sharp pins) was 1800 pins per square foot, pin diameter 0.062 in.TABLE 10 Properties Board 18 Board 19 Set time, min. 12.0 13.0Thickness, inch 0.545 0.545 Density, pcf 16.9 17.2 Weight, lb/MSF 765782 Water evaporation, 1550 1508 lb/MSF Estimated NRC 0.61 0.53

As shown in Table 10, the sample boards have densities lower than 20 pcfand acceptable NRC values.

EXAMPLE 7

Low density acoustical gypsum board—assessment of paper cover sheetsincluding a non-foamed bonding layer applied to the set gypsumcore-contacting surfaces

Two sets of three boards each were prepared using the following coreformulation to make the slurry (solids by weight %): stucco 84.5%perlite 5.0% paper fiber (hydropulp) 7.5% pregelatinized corn starch3.0%.

A soap foam having a foam density of 5.0 pcf was used. Additionaladditives were included in addition to the above total solids: CSA at0.5% by weight based on total solids; Borem at 0.1% by weight based ontotal solids; and sodium trimetaphosphate at 0.1% by weight based ontotal solids. The water/solids ratio was 2.4:1. The first set (Set A) ofsample boards was cast, and perforated (except at 0.375 in. depth), asin Step 2 of Example 2. For the second set (Set B) of sample boards,prior to casting, a non-foamed bonding layer (prepared from the samecore formulation without foam) was manually applied to the set gypsumcore-contacting surfaces of both the back paper and the face paper usinga 4.0 inch wide brush, then the second set (Set B) of sample boards wascast, and perforated (except at 0.375 in. depth), as in Step 2 ofExample 2. The set time was approx. 11.0 min. for all boards cast. Inthe following Table 11, the results are presented as average values.TABLE 11 Properties Set A Set B Thickness, inch 0.545 0.545 Density, pcf21.7 22.0 Water evaporation, 1787 1668 lb/MSF Estimated NRC 0.46 0.48

The boards of Set B possessed an excellent bond to the paper coversheets and to the set gypsum core after the board was dried. As shown inTable 11, the bond between the set gypsum core and the paper coversheets was significantly improved, without adversely affecting estimatedNRC after perforation of the face paper. The presence of the non-foamedbonding layer provided a better bond between the paper cover sheets andthe set gypsum core in the low density acoustical gypsum boards of thepresent invention, with no adverse effect on estimated NRC values afterperforation of the top surface cover sheet (face paper). The lowerestimated NRC values in both sets of boards (Sets A and B) were due tothe lower perforation depth.

EXAMPLE 8

Resistance to permanent deformation—assessment of low density acousticalgypsum board sag resistance

The low density acoustical gypsum boards made according to Examples 3-6demonstrated resistance to permanent deformation such as sag. Sag wastested in 2×4 foot board samples as follows. 3 inch wide×24 inch longstrips of board were cut from the aforementioned samples and testedunder 104° F./95% R.H. conditions. The board strips were laid in ahorizontal position on two ¼ inch wide supports, attached to a supportframe, whose length extended the full 3 inch width of the board, withone support at each end of the board. The 3 inch wide ends in contactwith the support frame were weighted down against the supports orclamped to the supports. The board strips remained in this position fora specified period of time (in this example, 3 days) under continuoussurrounding conditions of 104° F. and 95% relative humidity. The extentof sag of the board (sag deflection) was then determined by measuringthe distance in inches of the center of the top surface of the boardfrom the imaginary horizontal plane extending between the top edges ofthe ends of the board, i.e., a plane corresponding to the surface of theboard before exposure to the test conditions. After a 3 day test period,sag deflection for the test strips was measured in the range 0.122-0.218inch, which is substantially superior to known conventional ceilingpanels, in which sag deflection is normally 0.3-0.5 inch under the sametest conditions.

The low density acoustical gypsum boards made according to Examples 3-6passed the indicative flame spread test and met the Class-A rating.

The low density acoustical gypsum boards made according to Examples 3-6were tested for MOR strength (psi). The average MOR strength achievedwas about 200 psi, or greater.

The low density acoustical gypsum boards made according to Examples 3-6were less friable than conventional acoustical panels. Cutability,including edge detail, of these low density acoustical gypsum boards wasgood using a mechanical cutting saw. Edge detail, namely a lip, wasintroduced by grinding.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. Recitation of ranges of values herein are merely intended toserve as a shorthand method of referring individually to each separatevalue falling within the range, unless otherwise indicated herein, andeach separate value is incorporated into the specification as if it wereindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orotherwise clearly contradicted by context. The use of any and allexamples, or exemplary language (e.g., “such as”) provided herein, isintended merely to better illuminate the invention and does not pose alimitation on the scope of the invention unless otherwise claimed. Nolanguage in the specification should be construed as indicating anynon-claimed element as essential to the practice of the invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention. Itshould be understood that the illustrated embodiments are exemplaryonly, and should not be taken as limiting the scope of the invention.

1. A gypsum-based acoustical board having a set gypsum core disposedbetween two substantially parallel cover sheets comprising: a set gypsumcore made from a core formulation having about 75% to about 90% byweight stucco based on the total weight of the core formulation, about 0to about 15% by weight perlite based on the total weight of the coreformulation, about 2% to about 12% by weight paper fiber based on thetotal weight of the core formulation, and about 0.5% to about 5% byweight starch based on the total weight of the core formulation; and amultiplicity of sound-absorbing perforations extending through a coversheet and into the set gypsum core.
 2. The acoustical board of claim 1,wherein the core formulation includes stucco in an amount from about 80%to about 85% by weight based on the weight of the core formulation,perlite in an amount from about 5% to about 8% by weight based on theweight of the core formulation, paper fiber in an amount from about 6%to about 10% by weight based on the weight of the core formulation, andstarch in an amount from about 0.5% to about 2% by weight based on theweight of the core formulation.
 3. The acoustical board of claim 1,wherein the perlite has a density of from about 3.0 pcf to about 5.0pcf.
 4. The acoustical board of claim 1, wherein the paper fiber ishydropulp.
 5. The acoustical board of claim 1, wherein the starch ispregelatinized corn starch.
 6. The acoustical board of claim 1,including cover sheets comprising a face paper and a back paper, theperforations extending through the face paper and into but not throughthe set gypsum core.
 7. The acoustical board of claim 6, wherein theface paper has a pattern that creates a visual appearance of a texturewhen viewed from a distance.
 8. The acoustical board of claim 1, whereinthe perforations have a diameter of about 0.062 inch and are present atabout 1800 pins per square foot.
 9. The acoustical board of claim 1,wherein the board is about 0.54 inch thick and the perforations are fromabout ¼ inch to about ½ inch deep.
 10. The acoustical board of claim 1,wherein the board density is from about 16 pcf to about 20 pcf.
 11. Theacoustical board of claim 1, wherein the board density is from about 16pcf to about 17 pcf.
 12. The acoustical board of claim 1 having an NRCvalue from about 0.50 to about 0.65.
 13. The acoustical board of claim 1wherein the perlite in the core formulation is present at a weight ratioof perlite to paper fiber of about 1:1.1 to about 1:2.
 14. Theacoustical board of claim 1 wherein the perlite in the core formulationis present at a weight ratio of perlite to paper fiber of about 1:1.4 toabout 1:1.6.
 15. A gypsum-based acoustical board having a set gypsumcore disposed between a face paper and a back paper comprising: a setgypsum core made from a core formulation having about 75% to about 90%by weight stucco based on the total weight of the core formulation,about 0 to about 15% by weight perlite based on the total weight of thecore formulation, about 2% to about 12% by weight paper fiber based onthe total weight of the core formulation, and about 0.5% to about 5% byweight starch based on the total weight of the core formulation; and amultiplicity of sound-absorbing perforations extending through the facepaper and into but not through the set gypsum core.
 16. A method ofmaking gypsum-based acoustical board, comprising the steps of: (a)mixing a slurry of water, stucco in an amount from about 75% to about90% by weight based on the total solids weight, perlite in an amount upto about 15% by weight based on the total solids weight, paper fiber inan amount from about 2% to about 12% by weight based on the total solidsweight, and a starch in an amount from about 0.5% to about 5% by weightbased on the total solids weight; (b) adding a soap foam having adensity of about 10 pcf to the slurry; (c) depositing the slurry on afirst cover sheet; (d) maintaining the slurry under conditionssufficient for the stucco to form a set gypsum core; (e) placing asecond cover sheet over the set gypsum core to form an acoustical board;(f) drying the formed board; (g) cutting the dried board; and (h)perforating one of the cover sheets of the dried board in such a mannerthat the perforations extend into but not through the set gypsum core.17. The method of claim 16, further comprising applying a pattern on thesecond cover sheet prior to step (g).
 18. A method of makinggypsum-based acoustical board, comprising the steps of: (a) mixing aslurry comprising water, stucco in an amount from about 75% to about 90%by weight based on the total solids weight, perlite in an amount up toabout 15% by weight based on the total solids weight, paper fiber in anamount from about 2% to about 12% by weight based on the total solidsweight, and a starch in an amount from about 0.5% to about 5% by weightbased on the total solids weight; (b) adding a soap foam having adensity of about 10 pcf to the slurry; (c) depositing the slurry on afirst cover sheet; (d) maintaining the slurry under conditionssufficient for the stucco to form a set gypsum core; (e) placing asecond cover sheet over the set gypsum core to form an acoustical board;(f) drying the formed board to constant weight to produce a dried boardhaving a density of not more than about 20 pcf; (g) cutting the driedboard; and (h) perforating one of the cover sheets of the dried boardusing pins with a pin count of about 1800 pins per square foot and a pindiameter of about 0.062 inch, in such a manner that the perforationsextend into but not through the set gypsum core.
 19. The method of claim18, further comprising applying a pattern on the second cover sheetprior to step (g).